The Advanced Baseline Imager (ABI) is a passive imaging radiometer on-board National Oceanic and Atmospheric Administration’s (NOAA) Geostationary Operational Environmental Satellites-R (GOES-R) series. Its bands 7 to 16 are categorized as infrared (IR) bands, sampling within a spectral range of 3.9 to 13.3 μm in mid-wave infrared (MWIR) and long-wave infrared (LWIR) regions. ABI provides variable area imagery and radiometric information of Earth’s surface, atmosphere, and cloud cover. All of the IR bands are calibrated on-orbit in reference to an internal blackbody. While the ABI aboard the GOES-16 satellite has been working properly, an anomaly with GOES-17 ABI’s cooling system, specifically its loop heat pipe (LHP) subsystem, prevents heat from being efficiently transferred from the ABI electronics to the radiator to be dissipated into space. As a consequence, the heat accumulates inside the instrument, so the temperatures of its key components for IR calibration, including the focal plane modules (FPMs), scan mirrors, and blackbody, cannot be maintained at their designed operational levels. As an example, the temperatures of MWIR and LWIR FPMs, where IR detectors are located, are currently operated at a baseline temperature of ∼20 K warmer than the design and vary by as many as 27 K diurnally. This causes severe degradation to the data quality of ABI IR Level 1b radiance and subsequent Level 2+ products during the hot period of the day. Significant progress has been made to mitigate the effects of the LHP anomaly to optimize the IR performance of GOES-17 ABI. We summarize the efforts made by NOAA’s GOES-R Calibration Working Group, working collaboratively with other teams, to evaluate and alleviate the negative impacts of warmer and floating FPM temperatures on ABI IR calibration, and assess the IR performance accordingly.
Two flight models of the Advanced Baseline Imager (ABI) are in-orbit on the GOES-16 and GOES-17 geostationary satellites, with two more planned to be launched on GOES-T (2021) and GOES-U (2024). The ABI is the primary Earthviewing weather imaging instrument on the GOES-R Series, producing Level 1b (L1b) radiances and Cloud and Moisture Imagery (CMI) data products. The ABI L1b product is the source for all the ABI Level 2+ (L2+) products, including CMI, which makes the maturity process for these two products important. CMI is the only key performance parameter (KPP) of the GOES-R Series mission and thus CMI takes precedence over other ABI L2+ products. As the only KPP, CMI follows the same maturity schedule as the ABI L1b product. For the ABI L1b and CMI data products to be declared operational, they must pass through a series of calibration and validation tests and analyses, with the peerreviewed results showing that the instruments and products have achieved each level of maturity consistent with mission success. This paper describes the assessment process, the definitions of the product validation maturity levels, and an overview of the product performance for each instrument at each validation level. Additionally, this paper will describe planned programmatic changes aimed at streamlining the maturity process for the upcoming GOES-T and GOES-U satellites.
The GOES-17 Advanced Baseline Imager (ABI) has an anomaly with its on-board cooling system that prevents it from maintaining its Focal Plane Modules (FPMs) at cold, optimal temperatures. Because of this, during certain times of the year the FPMs and their detectors warm and cool throughout the day. Changing the detectors’ temperature changes their response to incoming radiance, which leads to calibration errors over time and degrades the imagery. Numerous mitigation strategies have been implemented to reduce the solar insolation on the instrument and to mitigate image degradation, including semi-annual yaw flips and changing the integration time of the detectors twice daily. These and other mitigations all work with the baseline calibration algorithms currently in place on the GOES-R Ground System. In an attempt to reduce the image degradation even further, the ABI vendor designed a new calibration scheme that predicts key parameters forward in time to account for the drifting FPM temperatures. These parameters, the linear gain term and dark current scene, are nominally updated on orbit every 5 minutes and 30 seconds, respectively. However, even at these relatively short cadences the detectors can change temperature, thereby rendering the parameters invalid for accurate calibration. By projecting these parameters forward in time the radiometric bias is reduced and image quality improves. This Predictive Calibration modification was deployed to operations on July 25, 2019, following several months of extensive testing and optimization by the GOES-R science teams. During this time several parameters and thresholds were tuned to ensure Predictive Calibration was turning on and off at the optimal times. Since going into operations users have seen noticeable improvement to the imagery and its calibration. This paper will discuss the fundamental assumptions behind the baseline equations and highlight the changes introduced by Predictive Calibration. Results will show the improvements to the calibration of the operational L1b products and reduction in image degradation.
As part of the geolocation accuracy assessment of lightning flashes detected by the Geostationary Lightning Mapper (GLM) on the GOES-16 and GOES-17 satellites (Geostationary Operational Environmental Satellite), two satellite laser ranging stations employed laser beacon systems to generate transient light pulses that simulate natural lightning around 777.4 nm to validate the pre-launch spec of 5 km. The pulse width, repetition rate, wavelength, and power of the laser-pulses were configured to produce sufficient instrument response to be detected as synthetic lightning events by the GLM instrument. During the testing period from April 2017 to January 2018, the laser systems illuminated the GOES-16 satellite to observe diurnal variation of the GLM system response, with particular emphasis on geolocation accuracy. The final GOES-16 laser beacon tests, which used the latest updates of the geolocation algorithms implemented by the GOES-R Ground Segment, showed the offsets between the GLM geolocated location and the known laser locations were within 5 km.
The first satellite of the Geostationary Operational Environmental Satellite-R series (GOES-R), the next generation of NOAA geostationary environmental satellites, was launched November 19, 2016. This satellite, GOES-16, carries six instruments dedicated to the study of the Earth’s weather (ABI), lightning mapping (GLM), solar observations (EXIS and SUVI), and space weather monitoring (SEISS and MAG). Each of these six instruments are in the process of going through a series of specialized calibration plans to achieve their product quality requirements. In this review paper we will describe the overall status of the on-orbit calibration program, the path forward to Full product validation status, and any changes that may occur for the cal/val plans for GOES-S, which is planned for launch in early 2018.
Lunar observations by the Suomi-NPP instrument VIIRS are scheduled on a nearly monthly basis at a phase angle of approximately -51 degrees. The lunar images acquired during scheduled observations have been used for radiometric calibration stability monitoring of the reflective solar bands, band-to-band registration characterization, modulation transfer function derivation and electric crosstalk examination. A satellite roll maneuver is usually necessary for the Moon to be viewed by VIIRS detectors, which results in the loss of approximately 20-minute science data during the period. Without any scheduling, the Moon has also been regularly observed when it intrudes the field of view of the instrument’s space view port. Since the launch of Suomi-NPP in late 2011, nearly 200 unscheduled lunar observations have been made with complete lunar images captured by at least two spectral bands. These observations are made at a larger phase angle from -45 to -90 degrees and libration angle range than the scheduled lunar observation. In this paper, the strategies and methodologies of lunar calibration developed for scheduled lunar observations are applied to these unscheduled lunar observations, with necessary adaptation to account for the differences in data format. The result from the unscheduled lunar observations are provided, with the focus of it comparison with the results from scheduled lunar observations as well as solar diffuser (SD) calibration. Overall, the long-term trends of these results agree with each other and the trends from the un-scheduled lunar calibration show more fluctuation. For radiometric calibration, the difference between the lunar calibration and SD calibration strongly depends on phase angles and libration angles. If the VIIRS measurement is accurate, this indicates that the lunar irradiance reference for the radiometric calibration, modeled by the USGS robotic lunar observatory (ROLO), carries systematic error that changes with these photometric factors. An empirical correction is applied to derive the relationship between the error and the phase angle to compensate the impact. The trends after the correction shows much less fluctuation to a level similar to the trends from scheduled calibration..
Jon Fulbright, Elizabeth Kline, David Pogorzala, Wayne MacKenzie, Ryan Williams, Kathryn Mozer, Dawn Carter, Randall Race, Jamese Sims, Matthew Seybold
The Geostationary Operational Environmental Satellite-R series (GOES-R) will be the next generation of NOAA geostationary environmental satellites. The first satellite in the series is planned for launch in November 2016. The satellite will carry six instruments dedicated to the study of the Earth’s weather, lightning mapping, solar observations, and space weather monitoring. Each of the six instruments require specialized calibration plans to achieve their product quality requirements. In this talk we will describe the overall on-orbit calibration program and data product release schedule of the GOES-R program, as well as an overview of the strategies of the individual instrument science teams. The Advanced Baseline Imager (ABI) is the primary Earth-viewing weather imaging instrument on GOES-R. Compared to the present on-orbit GOES imagers, ABI will provide three times the spectral bands, four times the spatial resolution, and operate five times faster. The increased data demands and product requirements necessitate an aggressive and innovative calibration campaign. The Geostationary Lightning Mapper (GLM) will provide continuous rapid lightning detection information covering the Americas and nearby ocean regions. The frequency of lightning activity points to the intensification of storms and may improve tornado warning lead time. The calibration of GLM will involve intercomparisons with ground-based lightning detectors, an airborne field campaign, and a ground-based laser beacon campaign. GOES-R also carries four instruments dedicated to the study of the space environment. The Solar Ultraviolet Imager (SUVI) and the Extreme Ultraviolet and X-Ray Irradiance Sensors (EXIS) will study solar activity that may affect power grids, communication, and spaceflight. The Space Environment In-Situ Suite (SEISS) and the Magnetometer (MAG) study the in-situ space weather environment. These instruments follow a calibration and validation (cal/val) program that relies on intercomparisons with other space-based sensors and utilize special spacecraft maneuvers. Given the importance of cal/val to the success of GOES-R, the mission is committed to a long-term effort. This commitment enhances our knowledge of the long-term data quality and builds user confidence. The plan is a collaborative effort amongst the National Oceanic and Atmospheric Administration (NOAA), the National Institute of Standards and Technology (NIST), and the National Aeronautics and Space Administration (NASA). It is being developed based on the experience and lessons-learned from the heritage GOES and Polar-orbiting Operational Environmental Satellite (POES) systems, as well as other programs. The methodologies described in the plan encompass both traditional approaches and the current state-of-the-art in cal/val.
The first VIIRS instrument was launched on-board the S-NPP satellite in October 2011. It has a total of 15 reflective solar bands (RSB), which include a day-night band (DNB). The VIIRS RSB are calibrated each orbit by an on-board solar diffuser and regularly scheduled lunar observations. With a few exceptions, regularly scheduled lunar observations have been made with the same phase angles from -51.5⁰ to -50.5⁰. The PLEIADES system consists of two satellites, PLEIADES-1A and PLEIADES-1B, which were launched in December of 2011 and December of 2012, respectively. Each instrument has 5 RSB: four (blue, green, red and near-infrared) bands with a 2.8 m spatial resolution and one panchromatic band with a 70 cm vertical viewing resolution. PLEIADES RSB are calibrated using observations of Pseudo Invariant Calibration Sites (PICS) and the Moon. Both PLEIADES-1A and PLEIADES-1B lunar observations have been made over a wide range of phase angles. In this paper we provide an overview of S-NPP VIIRS and PLEIADES lunar observations and an analysis to qualify their lunar calibration differences. Results derived from different inter-comparison methodologies (or approaches) are illustrated. Also discussed in this paper are the challenging issues, lessons, and future effort to further improve sensor lunar calibration inter-comparisons.
Both MODIS and VIIRS use a solar diffuser (SD) to calibrate their reflective solar bands (RSB), covering wavelengths from 0.41 to 2.3 μm. On-orbit changes of the SD bi-directional reflectance factor (BRF) are tracked by an on-board solar diffuser stability monitor (SDSM). The current SDSM design only covers the spectral range from 0.41 to 0.93 μm. In general, the SD degradation is strongly wavelength-dependent with larger degradation occurring at shorter wavelengths, and the degradation in the SWIR region is expected to be extremely small. As each mission continues, however, the impact due to SD degradation at SWIR needs to be carefully examined and the correction if necessary should be applied in order to maintain the calibration quality. For Terra MODIS, alternative approaches have been developed and used to estimate the SD degradation for its band 5 at 1.24 μm and a time-dependent correction has already been applied to the current level 1B (L1B) collection 6 (C6). In this paper, we present different methodologies that can be used to examine the SD degradation and their applications for both Terra and Aqua MODIS and S-NPP VIIRS SWIR calibration. These methodologies include but not limited to the use of lunar observations, Pseudo Invariant Calibration Sites (PICS), and deep convective clouds (DCC). A brief description of relative approaches and their use is also provided in this paper.
Both MODIS and VIIRS instruments use a solar diffuser (SD) for their reflective solar bands (RSB) on-orbit calibration. On-orbit changes in SD bi-directional reflectance factor (BRF) are tracked by a solar diffuser stability monitor (SDSM) using its alternate measurements of the sunlight reflected off the SD panel and direct sunlight through a fixed attenuation screen. The SDSM calibration data are collected by a number of filtered detectors, covering wavelengths from 0.41 to 0.94μm. In this paper we describe briefly the Terra and Aqua MODIS and S-NPP VIIRS SDSM on-orbit operation and calibration activities and strategies, provide an overall assessment of their SDSM on-orbit performance, including wavelength-dependent changes in the SDSM detector responses and changes in their SD BRF, and discuss remaining challenging issues and their potential impact on RSB calibration quality. Due to different launch dates, operating configurations, and calibration frequencies, the Terra and Aqua MODIS and S-NPP VIIRS SD have experienced different amount of SD degradation. However, in general the shorter the wavelength, the larger is the SD on-orbit degradation. On the other hand, the larger changes in SDSM detector responses are observed at longer wavelengths in the near infrared (NIR).
Lunar observations have been regularly scheduled for the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite since its launch on October 28th, 2011. In reference to the ROLO irradiance model, the detector gain coefficient or F-factor can be derived from these lunar observations for the reflective solar bands (RSB). Unlike its predecessor Moderate Resolution Imaging Spectroradiometer (MODIS), the Moon and the on-board solar diffuser (SD) are viewed by VIIRS detectors at the same angle of incidence (AOI) to the half angle mirror (HAM). Eliminating the impact from the variation in the instrument response to the HAM AOI, this design allows the detector gain changes tracked by the Moon and the SD to be directly compared. In this paper, we update the lunar F-factors from the scheduled lunar calibration. The long-term trends of the lunar F-factor trending and the SD F-factor trending still agree in general for all RSBs. We also calculate the lunar F-factor at detector level and compare the detector dependency of the lunar F-factor and the SD F-factor. For a few RSBs at shorter wavelengths, a bias of up to 1% between the two has been identified. Using the detector-dependent lunar F-factors will decrease the retrieved Earth view radiance of lower-number detectors in relative to higher-number detectors than the SD F-factors. The inconsistency indicates systematic bias between the lunar and SD calibration approaches.
Observations of stars can be used to calibrate the radiometric performance of the Day/Night Band (DNB) of the Suomi-NPP instrument VIIRS. Bright stars are normally visible in the Space View window. In this paper, we describe several potential applications of stellar observations with preliminary results for several. These applications include routine trending of the gain of the highand mid-gain stages of the DNB and trending the gain ratio between those stages. Many of the stars observed by the VIIRS DNB have absolute flux curves available, allowing for an absolute calibration. Additionally, stars are visible during scheduled lunar roll observations. The electronic sector rotations applied during the scheduled lunar observations greatly increases the sky area recorded for a brief period, increasing the observing opportunities. Additionally, the DNB recorded data during the spacecraft pitch maneuver. This means the deep sky was viewed through the full Earth View. In this situation, thousands of stars (and the planet Mars) are recorded over a very short time period and over all aggregation zones. A possible application would be to create a gain curve by comparing the instrument response to the known apparent stellar brightness for a large number of stars of similar spectral shape. Finally, the DNB is especially affected the mirror degradation afflicting VIIRS. The degradation has shifted peak of the relative spectral response (RSR) of the DNB the blue and the effective band pass has been slightly reduced. The change in response for hot stars (effective temperatures of over 30,000 K) due to this degradation will differ by about 10 percent from the response change of cool stars (below 3500 K).
Due to a software error, the solar and lunar vectors reported in the on-board calibrator intermediate product (OBC-IP) files for SNPP VIIRS are incorrect. The magnitude of the error is about 0.2 degree, and the magnitude is increasing by about 0.01 degree per year. This error, although small, has an effect on the radiometric calibration of the reflective solar bands (RSB) because accurate solar angles are required for calculating the screen transmission functions and for calculating the illumination of the Solar Diffuser panel. In this paper, we describe the error in the Common GEO code, and how it may be fixed. We present evidence for the error from within the OBC-IP data. We also describe the effects of the solar vector error on the RSB calibration and the Sensor Data Record (SDR). In order to perform this evaluation, we have reanalyzed the yaw-maneuver data to compute the vignetting functions required for the on-orbit SD RSB radiometric calibration. After the reanalysis, we find effect of up to 0.5% on the shortwave infrared (SWIR) RSB calibration.
Lunar observations by the Suomi-NPP instrument VIIRS help improve our understanding of the radiometric calibration of the reflected solar bands (RSB). The spacecraft performs a scheduled roll maneuver approximately nine times per year to acquire lunar data at nearly constant phase angles. The instrument also captures lunar radiometric data at other times when the instrument Space View port serendipitously points at the Moon. In this paper, we present results only from the scheduled Moon observations, comparing the observed lunar irradiance to ROLO model results to provide calibration coefficients for each band, mirror side, and detector. These results can be evaluated directly to the primary RSB calibration method derived from the Solar Diffuser. This paper also discusses recent improvements to our methodology for measuring the lunar irradiance, including a new method for determining the lunar position within the field of view, an all-detector calibration methodology, and an assessment of the uncertainties in our lunar observations. This paper includes lunar observation data through June 2014.
Terra and Aqua MODIS have successfully operated for more than 13 and 11 years since their launch in 1999 and 2002,
respectively. The VIIRS instrument on-board the S-NPP launched in 2011 has also operated for nearly 2 years. Both
MODIS and VIIRS make observations in the reflective solar and thermal emissive regions and their on-orbit calibration
and characterization are provided by a set of on-board calibrators (OBC). In addition, lunar observations have been made
on a regular basis to support sensor on-orbit calibration. This paper provides a brief overview of MODIS and VIIRS
instrument on-orbit calibration and characterization activities. It describes the approaches and strategies developed to
schedule and perform on-orbit lunar observations. Specific applications of MODIS and VIIRS lunar observations
discussed in this paper include radiometric calibration stability monitoring and performance assessment of sensor spatial
characterization. Results derived from lunar observations, such as sensor response (or gain) trending and band-to-band
registration, are compared with that derived from sensor OBC. The methodologies and applications presented in this
paper can also be applied to other earth observing sensors.
The Visible/Infrared Imager Radiometer Suite (VIIRS) instrument aboard the Suomi National Polarorbiting Partnership (SNPP) satellite performs its radiometric calibration in the reflective solar bands (RSB) wavelength region primarily through observing the sunlight scattered from the onboard Solar Diffuser (SD). The degradation (over time) of the SD reflectance is determined by the onboard Solar Diffuser Stability Monitor (SDSM). The SDSM detector relative spectral response (RSR) over the out-ofband (OOB) wavelength region leads to a non-negligible bias to the originally determined SD degradation coefficient over wavelengths from 412 nm to 488 nm. In this Proceeding, we consider the out-of-band contribution to determine the bias. Our computation shows that the bias to the degradation coefficient is larger at a shorter wavelength and increases with time. On the 564th day after launch (~ orbit 8000), at a wavelength of 412 nm, the bias (OOB-corrected – not-OOB-corrected) has a mean of -0.021, and at a wavelength of 445 nm, the bias has a mean of -0.009.
The VIIRS instrument on Suomi-NPP performs its primary radiometric calibration using the Solar Diffuser, which degrades with exposure to UV light. The Solar Diffuser is monitored by the Solar Diffuser Stability Monitor. In this paper, we evaluate potential improvements to the algorithms that generate the resulting H-factors, including updates to the screen transmission functions and new methodologies to increase the amount of useful data. We also track the on-orbit degradation of the SDSM detectors and predict the long-term performance of the sensors.
Both VIIRS and MODIS instruments use solar diffuser (SD) and lunar observations to calibrate their reflective solar bands (RSB). A solar diffuser stability monitor (SDSM) is used to track the SD on-orbit degradation. On-orbit observations have shown similar wavelength-dependent SD degradation (larger at shorter VIS wavelengths) and SDSM detector response degradation (larger at longer NIR wavelengths) for both VIIRS and MODIS instruments. In general, the MODIS scan mirror has experienced more degradation in the VIS spectral region whereas the VIIRS rotating telescope assembly (RTA) mirrors have seen more degradation in the NIR and SWIR spectral region. Because of this wavelength dependent mirror degradation, the sensor’s relative spectral response (RSR) needs to be modulated. Due to differences between the solar and lunar spectral irradiance, the modulated RSR could have different effects on the SD and lunar calibration. In this paper, we identify various factors that should be considered for the improvements of VIIRS and MODIS solar and lunar calibration and examine their potential impact. Specifically, we will characterize and assess the calibration impact due to SD and SDSM attenuation screen transmission (uncertainty), SD BRF uncertainty and onorbit degradation, SDSM detector response degradation, and modulated RSR resulting from the sensor’s optics degradation. Also illustrated and discussed in this paper are the calibration strategies implemented in the VIIRS and MODIS SD and lunar calibrations and efforts that could be made for future improvements.
Launched in December 1999 and May 2002, Terra and Aqua MODIS have successfully operated for more than 12 and
10 years, respectively. MODIS reflective solar bands (RSB) are calibrated on-orbit by a solar diffuser (SD). Its on-orbit
degradation, or the change in its bi-directional reflectance factor (BRF), is tracked by a solar diffuser stability monitor
(SDSM). The MODIS SDSM makes alternate observations of direct sunlight through an attenuation screen (Sun view)
and of sunlight reflected diffusely off the SD (SD view) during each SDSM calibration event. The MODIS SDSM has 9
detectors, covering wavelengths from 0.41 to 0.94 μm. Due to a design error in MODIS SDSM sub-system (identified
post-launch), relatively large ripples were noticed in its Sun view responses. As a result, an alternative approach was
developed by the MODIS calibration team to minimize the uncertainty in determining the SD on-orbit degradation. The
first VIIRS, on-board the Suomi NPP spacecraft, was successfully launched in October 2011. It carries a MODIS-like
SD and SDSM system for its RSB on-orbit calibration. Its design was improved based on lessons learned from MODIS.
Operationally, the VIIRS SDSM is used more frequently than MODIS. VIIRS SDSM collects data using 8 individual
detectors, covering a similar wavelength range as MODIS. This paper provides an overview of MODIS and VIIRS
SDSM design features, their on-orbit operations, and calibration strategies. It illustrates their on-orbit performance in
terms of on-orbit changes in SDSM detector on-orbit responses and on-orbit degradations of their SD. Results show that
on-orbit changes of both MODIS and VIIRS SD BRF and SDSM response have similar wavelength dependency: the SD
degradation is faster at shorter visible wavelengths while the decrease of SDSM detector responses (gains) is greater at
longer near-infrared wavelengths.
The Visible-Infrared Imaging Radiometer Suite (VIIRS) was launched onboard the Suomi National Polar-orbiting
Partnership (NPP) spacecraft on October 28, 2011. Among the bands on VIIRS are 14 reflective solar bands (RSBs).
The RSBs are calibrated using the sun as a source, after attenuation and reflection of sunlight from a Solar Diffuser (SD).
The reflectance of the SD is known to degrade over time, particularly at the blue end of the visible spectrum. VIIRS
incorporates a separate instrument, a Solar Diffuser Stability Monitor (SDSM), in order to measure and trend the SD
Bidirectional Reflectance Distribution Function BRDF changes over time. Inadequate knowledge of the SDSM screen
transmission as a function of solar geometry and SDSM detector dependent modulation effects require a unique
processing methodology to eliminate unphysical artifacts from the SD BRDF trending. The unique methodology is used
to generate periodic updates to operational Look-up Tables (LUTs) used by the Sensor Data Record (SDR) operational
code to maintain the calibration of the RSBs. This paper will discuss on-orbit SD BRDF behavior along with the
processing methodology used to generate RSB LUT updates incorporating the trended SD BRDF behavior.
We describe the on-orbit characterization and performance of the Solar Diffuser Stability Monitor (SDSM) on-board
Suomi-NPP/VIIRS. This description includes the observing procedure of each SDSM event, the algorithms used to
generate the Solar Diffuser degradation corrective factors, and the results for the mission to date. We will also compare
the performance of the VIIRS SDSM and SD to the similar components operating on the MODIS instrument on the EOS
Terra and Aqua satellites.
The on-orbit radiometric response calibration of the VISible/Near InfraRed (VISNIR) and the Short-Wave InfraRed
(SWIR) bands of the Visible/Infrared Imager/Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting
Partnership (NPP) satellite is carried out through a Solar Diffuser (SD). The transmittance of the SD screen and the
SD’s Bidirectional Reflectance Distribution Function (BRDF) are measured before launch and tabulated, allowing
the VIIRS sensor aperture spectral radiance to be accurately determined. The radiometric response of a detector is
described by a quadratic polynomial of the detector’s digital number (dn). The coefficients were determined before
launch. Once on orbit, the coefficients are assumed to change by a common factor: the F-factor. The radiance
scattered from the SD allows the determination of the F-factor. In this Proceeding, we describe the methodology and
the associated algorithms in the determination of the F-factors and discuss the results.
The Suomi National Polar-orbiting Partnership (NPP) satellite was launched on Oct. 28, 2011, and began the
commissioning phase of several of its instruments shortly thereafter. One of these instruments, VIIRS, was found to
exhibit a gradual but persistent decrease in the optical throughput of several bands, with the near-infrared bands being
more affected than those in the visible. The rate of degradation quickly increased upon opening of the nadir door that
permits the VIIRS telescope to view the earth. Simultaneously, a second instrument on NPP, the Solar Diffuser Stability
Monitor (SDSM), was experiencing a similar decrease in response, leading the investigation team to suspect that the
cause must be the result of some common contamination process. This paper will discuss a series of experiments that
were performed to demonstrate that the VIIRS and SDSM response changes were due to separate causes, and which
enabled the team to conclude that the VIIRS sensor degradation was the result of ultraviolet light exposure of the
rotating telescope assembly. The root cause investigation of the telescope degradation will be addressed in a separate
paper.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.